JP6776656B2 - Manufacturing method of aluminum alloy material and manufacturing method of piston - Google Patents

Description

The present invention relates to an aluminum alloy material, a piston for an internal combustion engine, an internal combustion engine, a method for manufacturing an aluminum alloy material, and a method for manufacturing a piston.

The anodized film (also referred to as alumite) of an aluminum (Al) -based alloy has the characteristics of being extremely hard and having excellent corrosion resistance and wear resistance in a wide temperature range. Further, among the Al-based alloys, the hypereutectic alloy containing Al and silicon (Si) (hereinafter, also simply referred to as “Al—Si-based hypereutectic alloy”) has a smaller thermal expansion coefficient and further. It also has the property of having higher wear resistance. Therefore, the aluminum alloy material having the anodized film of the Al—Si hypereutectic alloy is preferably used for a member that is repeatedly subjected to thermal and mechanical loads such as a piston of an internal combustion engine.

For example, Patent Document 1 describes a piston for an internal combustion engine made of an Al—Si-based hypereutectic alloy. An anodized film having a thickness of 10 to 50 μm is formed on the inner surface of the top ring groove portion of the piston, and primary crystal Si particles having a size of 10 to 40 μm are dispersed and exposed on the surface of the anodized film. .. In Patent Document 1, by forming a hard anodized film on the inner surface of the top ring groove portion, wear of the inner surface and generation of scuff from the inner surface are suppressed, and further, dispersed exposure is provided from the surface of the anodized film. It is stated that the hard primary Si particles support the load from the mating material, thereby suppressing the wear of the anodized film.

Further, Patent Document 2 also describes a piston for an internal combustion engine made of an Al—Si-based hypereutectic alloy having a primary crystal Si particle size of 50 μm or less. An anodized film having a thickness of 30 to 150 μm is formed on the top of the piston. According to Patent Document 2, hard alumite can suppress the occurrence of cracks in the end of the combustion chamber of the piston, and the size of the primary crystal Si particles is made finer, so that the strength of the alumite layer is further increased. It is described as. Patent Document 2 describes that the size of primary crystal Si particles can be reduced to 50 μm or less by casting the melted Al—Si alloy at high pressure (at least 500 kg / cm ² ).

Japanese Unexamined Patent Publication No. 1-190951 Japanese Unexamined Patent Publication No. 61-229963

There is a demand for further improving the heat-shielding property of an aluminum-based alloy material having an anodized film formed from the above-mentioned Al—Si-based hypereutectic alloy. For example, if the aluminum-based alloy material with improved heat insulation is used for the piston for an internal combustion engine, it is considered that the cooling loss due to heat transfer from the combustion chamber to the inside of the piston can be suppressed and the fuel consumption of the internal combustion engine can be further reduced. Be done. If the fuel consumption of the internal combustion engine is lowered, it is expected that the burden on the environment can be reduced and the financial burden on the user can be reduced.

In view of the above circumstances, the present invention provides an aluminum-based alloy material having an anodic oxide film formed from an Al—Si-based hyperchromic alloy and having a higher heat-shielding property. It is an object of the present invention to provide a piston and an internal combustion engine using an aluminum alloy material, and to provide a method for manufacturing such an aluminum alloy material and a piston.

In one aspect of the present invention, the above object is the Al—Si based hypereutectic alloy in which the Al—Si based hypereutectic alloy and the primary crystal Si particles layer-separated in the film forming direction are dispersed on the surface or inside thereof. It is achieved by an aluminum alloy material including an anodized film of a crystal alloy, a piston for an internal combustion engine having the aluminum alloy material on the surface, and an internal combustion engine having the piston for an internal combustion engine.

In another aspect of the present invention, the above object is to sulfuric acid of 0.5 mol / L or more and 4.0 mol / L or less and 0.05 mol / L or more and 0.2 mol of Al—Si based hypereutectic alloy. A method for producing an aluminum alloy material that is anodized for 0.5 hours or more with an electrolytic solution containing an organic acid of / L or less, and a piston base material for an internal combustion engine cast from an Al—Si hypereutectic alloy. On the other hand, an electrolytic solution containing sulfuric acid of 0.5 mol / L or more and 4.0 mol / L or less and an organic acid of 0.05 mol / L or more and 0.2 mol / L or less is subjected to anodization treatment for 0.5 hours or more. Achieved by the method of manufacturing the piston for the internal combustion engine.

According to the present invention, an aluminum-based alloy material having an anodic oxide film formed from an Al—Si-based hypersynchronous alloy, which has a higher heat-shielding property, and such an aluminum-based alloy material are used. Pistons and internal combustion engines, as well as methods for manufacturing such aluminum alloys and pistons are provided.

FIG. 1A is a cross-sectional photograph of an aluminum-based alloy material according to an embodiment of the present invention. FIG. 1B is a cross-sectional photograph of another aluminum-based alloy material according to the above embodiment.

As a result of diligent research, the present inventor has developed a technique for layer-separating primary-crystal Si particles in an anodized film formed from an Al—Si-based hypereutectic alloy, and when the primary-crystal Si particles are layer-separated, the above-mentioned anode It was found that the heat-shielding property of the oxide film is further enhanced. That is, the aluminum-based alloy material according to the embodiment of the present invention contains an anodic oxide film, and is first dispersed on the surface or inside of the anodic oxide film as shown in FIGS. 1A and 1B, which are cross-sectional photographs thereof. Crystalline Si particles are layer-separated in the film formation direction of the anodized film. The layer-separated primary crystal Si particles contain air having a low thermal conductivity between the layers. Therefore, it is considered that the anodized film having the primary crystal Si particles separated by the layers has higher heat-shielding property than the conventional anodized film in which the primary crystal Si particles are not layer-separated. It is considered that the aluminum-based alloy material having has a higher heat-shielding property than the conventional aluminum-based alloy material.

A typical embodiment of the present invention will be described in detail below.

1. 1. Aluminum-based alloy material The aluminum-based alloy material according to the embodiment of the present invention includes an Al—Si based hypereutectic and an anodized film of the above Al—Si hypereutectic, and FIGS. 1A and 1B. As shown in the above, in the anodic oxide film, the primary crystal Si particles are layer-separated in the film formation direction of the anodic oxide film.

The Al—Si based hypereutectic alloy is an alloy containing Al and Si (Al—Si based alloy), and is a hypereutectic alloy having a higher Si content than the eutectic point. The Si content can be 10.5% by mass or more and 30.0% by mass or less. From the viewpoint of facilitating layer separation, the Si content is 10.5% by mass or more and 20.0% by mass or less, preferably 10.5% by mass or more and 15.0% by mass or less, more preferably 10.5. It can be mass% or more and 13.0 mass% or less, more preferably 11.0 mass% or more and 13.0 mass% or less.

The Al—Si based hypereutectic alloy may contain elements other than Al and Si. Examples of elements that can be contained in the Al—Si-based hypereutectic alloy include copper (Cu), nickel (Ni), magnesium (Mg), phosphorus (P), and the like.

The contents of Cu, Ni, and Mg in the Al—Si-based hypereutectic alloy are not limited as long as a sufficiently large primary crystal Si is produced, but for example, the content of Cu is 1.0 mass by mass. % Or more and 6.0% by mass or less, Ni content is 1.0% by mass or more and 3.5% by mass or less, Mg content is 0.1% by mass or more and 1.0% by mass or less. it can.

On the other hand, P is an element added to make the primary crystal Si smaller, but from the viewpoint of making it easier to separate the primary crystal Si in the present embodiment, the Al—Si based hypereutectic alloy The content of P in the above is preferably small, for example, 10 ppm or more and 120 ppm or less, preferably 10 ppm or more and 95 ppm or less, more preferably 10 ppm or more and 90 ppm or less, and further preferably 10 ppm or more and 80 ppm or less.

The ratio of each element in the aluminum-based alloy material can be measured by a known method such as emission spectroscopy.

The anodic oxide film is mainly made of aluminum oxide, which is formed by bringing the Al—Si-based hypereutectic alloy into contact with an electrolytic solution and energizing the electrolytic solution using the Al—Si-based hypereutectic alloy as an anode. It is a film used as an ingredient. Al is oxidized by the energization and the film grows in the direction of thickening. At this time, a part of Al is dissolved to form pores, and the Al—Si-based hypereutectic alloy is formed from the pores. The above film is also formed in the depth direction. Therefore, the anodized film is characterized by being eroded in the depth direction of the Al—Si-based hypereutectic alloy to form a film, and the pores extending in the film forming direction and the holes surrounding the pores. It has the characteristic that a wall can be formed. In the present invention, the film-forming direction of the anodized film (or simply the "film-forming direction") means the direction in which the film becomes thicker (the depth direction of the anodized film).

In the present embodiment, the primary crystal Si in the Al—Si-based hypersymbolic alloy is in a direction of extending in the film forming direction due to thermal expansion or current of aluminum or aluminum oxide when the anodized film is formed. It is considered that the layers are separated by cracking in the film forming direction due to the stress on the film. From the viewpoint of enhancing the heat-shielding effect of the aluminum-based alloy material by separating more primary crystal Si into layers or separating each primary crystal Si into finer layers, the anodic oxidation treatment for a longer time is performed. It is preferable to form an anodic oxide film having a thicker film thickness. From such a viewpoint, the film thickness of the anodized film is preferably 50 μm or more and 500 μm or less, more preferably 70 μm or more and 300 μm or less, and further preferably 120 μm or more and 250 μm or less.

The primary crystal Si is a phase of Si that precipitates when the Al—Si-based hypereutectic alloy that has been melted by heating is cooled. In the present embodiment, primary crystal Si layer-separated in the film forming direction is dispersed on the surface or inside of the anodized film. The primary crystal Si may be dispersed not only on the surface or inside of the anodized film but also in the region of the Al—Si-based hypereutectic alloy that does not constitute the anodized film.

From the viewpoint of increasing the size of the primary crystal Si to facilitate layer separation, while suppressing the decrease in the strength of the alloy due to the primary crystal Si being too large, the particle size of the primary crystal Si is, for example, 10 μm or more and 100 μm. It can be preferably 10 μm or more and 80 μm or less, and more preferably 20 μm or more and 50 μm or less.

The particle size of the primary crystal Si is, for example, the particle size of 20 primary crystal Si existing in an arbitrary cross section of the aluminum-based alloy material (additional average of the major axis and the minor axis). Can be calculated by calculating the added average of.

From the viewpoint of further enhancing the heat-shielding effect of the aluminum-based alloy material, it is preferable that a larger amount of the primary crystal Si is layer-separated. From such a viewpoint, when setting a region corresponding to the thickness of the anodized film having a width of 20 mm in the direction in which the surface of the anodized film extends in the cross section in the film forming direction of the anodized film, It is preferable that 15 or more regions in which at least one layer-separated primary crystal Si exists in the above regions are present in the 20 arbitrarily set regions.

Further, from the viewpoint of further enhancing the heat shielding effect of the aluminum-based alloy material, it is preferable that the primary crystal Si is more finely separated into layers. From such a viewpoint, when setting a region corresponding to the thickness of the anodized film having a width of 500 μm in the direction in which the surface of the anodized film extends in the cross section in the film forming direction of the anodized film, It is preferable that there are 12 or more regions in the above region in which the primary crystal Si layer-separated into 5 or more layers exists in the 20 arbitrarily set regions. At this time, the number of continuous layers occupying more than half of the width of the primary crystal Si in the direction substantially orthogonal to the film formation direction is defined as the number of layer-separated primary crystal Si layers.

The aluminum-based alloy material has a high heat-shielding effect. For example, the thermal conductivity of the aluminum-based alloy material is 0.15 W / mk or more and 0.65 W / mk or less, preferably 0.20 / mk or more and 0.40 W / mk or less, and more preferably 0.20 W / mk or more and 0. It can be .35 W / mk or less, more preferably 0.20 W / mk or more and 0.30 W / mk.

The thermal conductivity can be a value measured by a known unsteady method such as a laser flash method.

2. Piston for Internal Combustion Engine The piston for an internal combustion engine according to another embodiment of the present invention is a piston for an internal combustion engine containing at least a part of the surface of the aluminum alloy material according to the above-described embodiment. At this time, the aluminum-based alloy material is included in the piston for an internal combustion engine so that the anodized film is located on the surface side of the piston.

The piston for an internal combustion engine can suppress cooling loss and reduce the fuel consumption of the internal combustion engine due to the high heat shielding effect of the aluminum alloy material.

From the viewpoint of further suppressing the cooling loss due to heat transfer from the combustion chamber to the inside of the piston and further enhancing the heat shielding effect of the internal combustion engine piston, the internal combustion engine piston forms at least the top surface of the piston. It is preferable to have the anodic oxide film on a wall surface or a part of the wall surface forming the combustion chamber, and more preferably to have the anodic oxide film on the entire surface of the wall surface forming the top surface of the piston or the wall surface forming the combustion chamber. It is more preferable to have the anodized film on both the wall surface forming the top surface of the piston and the wall surface forming the combustion chamber, and the entire surface of both the wall surface forming the top surface of the piston and the wall surface forming the combustion chamber It is more preferable to have the anodized film. At this time, the anodized film may form the outermost layer of the piston, or another film may be formed on the surface of the anodized film.

The piston for an internal combustion engine may be a piston for a gasoline engine or a piston for a diesel engine. However, in a piston for a diesel engine having a characteristic that a problem of cooling loss is more likely to occur due to a wider combustion chamber, the aluminum-based alloy material is used. The reduction in fuel consumption due to the high heat shielding effect of the engine is more remarkable.

3. 3. Internal Combustion Engine The internal combustion engine according to another embodiment of the present invention is an internal combustion engine including a piston for an internal combustion engine according to the above-described embodiment. The internal combustion engine may include a plurality of pistons. At this time, at least one of the plurality of pistons may be the piston for the internal combustion engine, but all of the plurality of pistons are the pistons for the internal combustion engine. It is preferable to have.

In the internal combustion engine, the cooling loss is suppressed due to the high heat-shielding effect of the aluminum-based alloy material, and the fuel consumption of automobiles and the like can be reduced.

The internal combustion engine may be a gasoline engine or a diesel engine, but in a diesel engine piston having a characteristic that a problem of cooling loss is more likely to occur due to a wider combustion chamber, due to the high heat shielding effect of the aluminum-based alloy material. The reduction in fuel consumption is more noticeable.

4. Method for producing aluminum-based alloy material The aluminum-based alloy material has sulfuric acid of 0.5 mol / L or more and 4.0 mol / L or less and 0.05 mol / L or more and 0 of the above-mentioned Al—Si hypereutectic alloy. It can be produced by subjecting it to anodization treatment for 0.5 hours or more with an electrolytic solution containing an organic acid of .2 mol / L or less.

The Al—Si-based hypereutectic alloy is produced by cooling or pressure solidifying a molten alloy containing Al, Si and optionally containing Cu, Ni, Mg, P and other trace elements in a predetermined ratio. can do. The ratio of each of the above elements in the molten alloy may be, for example, the same as the composition of each of the above elements. The molten alloy may be prepared by heating each of the above-mentioned elements prepared individually and dissolving each other, or by dissolving standard products such as AC8A, AC9A and AC9B specified in JIS H5202. Good.

From the viewpoint of facilitating molding, pressure solidification is preferable. At this time, from the viewpoint of increasing the particle size of the primary crystal Si to facilitate layer separation, the pressing force applied to the molten alloy is 2.0 kg / cm ² or more and less than 1000 kg / cm ^2. Preferably, it is 2.0 kg / cm ² or more and less than 500 kg / cm ² , more preferably 2.0 kg / cm ² or more and less than 100 kg / cm ² , and 2.0 kg / cm ² or more and 50 kg / cm. It is more preferably less than ² .

At this time, by putting the molten alloy into a mold having the shape of a piston for an internal combustion engine and cooling or pressure-solidifying the molten alloy, the Al—Si-based hyperchromic alloy can be formed into the shape of a piston for an internal combustion engine. (In the present invention, an alloy formed in the shape of a piston for an internal combustion engine before being anodized is also referred to as a "piston base material for an internal combustion engine").

The anodic oxidation treatment is a known method of anodic oxidation treatment by bringing the Al—Si-based hypereutectic alloy into contact with an electrolytic solution and energizing the electrolytic solution using the Al—Si-based hypereutectic alloy as an anode. Can be applied with. At this time, the electrolytic solution contains sulfuric acid of 0.5 mol / L or more and 4.0 mol / L or less and an organic acid of 0.05 mol / L or more and 0.2 mol / L or less. The energization is performed for 0.5 hours or more.

The organic acid may be an organic acid usually used for anodization treatment, for example, an organic acid having two or more carboxyl groups. Examples of such organic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, maleic acid, itaconic acid, malic acid, tartaric acid and citric acid, among which oxalic acid and citric acid. preferable.

An electrolytic solution containing an inorganic acid such as sulfuric acid is often used for the anodizing treatment. However, according to the findings of the present inventor, when the anodizing treatment is performed using an electrolytic solution containing only sulfuric acid, primary crystal Si is hardly layer-separated. On the other hand, in the anodizing treatment using the electrolytic solution containing sulfuric acid and the organic acid, sufficient stress is applied to the primary crystal Si because the density of the anodized film is high, and layer separation is more likely to occur. .. Further, in the anodizing treatment using the electrolytic solution containing sulfuric acid and an organic acid, a stronger and more porous anodized film can be formed. Therefore, the anodized film thus produced can be preferably used for a member that is repeatedly subjected to thermal and mechanical loads, such as a piston of an internal combustion engine.

The concentration of the sulfuric acid may be 0.5 mol / L or more and 4.0 mol / L or less, and preferably 1.0 mol / L or more and 2.0 mol / L or less.

The concentration of the organic acid may be 0.05 mol / L or more and 0.2 mol / L or less, and preferably 0.08 mol / L or more and 0.15 mol / L or less.

The concentration ratio of the sulfuric acid to the organic acid is preferably (sulfuric acid concentration) / (organic acid concentration) = 1/20 or more and 1/5 or less, and (sulfuric acid concentration) / (organic acid concentration). Concentration) = 1/15 or more and 1/8 or less is more preferable.

The temperature of the electrolytic solution may be the same as the temperature at which the usual anodizing treatment is performed, and can be, for example, 0 ° C. or higher and 10 ° C. or lower, preferably 0 ° C. or higher and 4 ° C. or lower.

The current density of the current energization may be the same as the current density when performing the normal anodization treatment, for example, 2.0 A / dm ² or more and 30 A / dm ² or less, preferably 6 A / dm ² or more and 15 A / dm ^2. It can be as follows.

The above energization is performed for 0.5 hours or more. In the present embodiment, the energization is performed for 0.5 hours or more, and stress is applied to the primary crystal Si over a long period of time to sufficiently separate the primary crystal Si into layers. The energizing time can be determined according to the thickness of the anodized film to be produced, for example, 0.5 hours or more and 4.0 hours or less, preferably 0.5 hours or more and 3.0 hours or less, more preferably. Can be 0.5 hours or more and 1.5 hours or less, more preferably 0.5 hours or more and 1.0 hours or less.

The above-mentioned piston for an internal combustion engine can be manufactured by applying the anodic oxidation treatment by the above method to the piston base material for an internal combustion engine cast from the above-mentioned Al—Si-based hypereutectic alloy. From the viewpoint of producing a piston having a higher heat-shielding effect, the anodization treatment is preferably applied to at least a part of the wall surface forming the top surface of the piston or the wall surface forming the combustion chamber, and the top surface of the piston is applied. It is more preferably applied to the entire surface of the wall surface to be formed or the wall surface forming the combustion chamber, and more preferably to be applied to both the wall surface forming the top surface of the piston and the wall surface forming the combustion chamber, and forming the top surface of the piston. It is more preferable to apply it to the entire surface of both the wall surface and the wall surface forming the combustion chamber.

The aluminum alloy material and the piston for an internal combustion engine produced by the above method may be further subjected to post-treatment including trimming and finishing.

Hereinafter, specific examples of the present invention will be described together with comparative examples, but the present invention is not limited thereto.

1. 1. Preparation of test piece 1-1. Test piece 1
Circular shape (12.5 mmφ, thickness 2 mm) Al—Si-based hypersymbolic alloy (Si: 11.8% by mass, Cu: 3.5% by mass, Ni: 1.9% by mass, Mg: 0.8 Mass%, P: 90 ppm) was masked on one side and immersed in an electrolytic solution containing 1.5 mol / L sulfuric acid and 0.1 mol / L oxalic acid to obtain a current with a current density of 10 A / dm ^2. The electric current was applied for 50 minutes to obtain a test piece 1 having an anodized film on the unmasked surface.

1-2. Test piece 2
The Al—Si based hypereutectic alloy is used as an Al—Si based hypereutectic alloy having a different composition (Si: 13.0% by mass, Cu: 4.0% by mass, Ni: 2.1% by mass, Mg: 0. A test piece 2 having an anodic oxide film on one side was obtained in the same manner as the test piece 1 except that the content was .55% by mass and P: 45 ppm).

1-3. Test piece 3
A test piece 3 having an anodized film on one side was obtained in the same manner as the test piece 1 except that the energization time was 80 minutes.

1-4. Test piece 4
The electrolytic solution was an electrolytic solution containing 2.0 mol / L sulfuric acid but substantially free of organic acids, and an anodic oxide film was formed on one side in the same manner as in Test Piece 1 except that the energization time was 15 minutes. A test piece 4 having the above was obtained.

2. Measurement and evaluation From the photomicrographs obtained by cutting the test pieces 1 to 4 and photographing the cross section at a magnification of 1000 times, the particle size of the primary crystal Si dispersed on the surface or inside of the anodic oxide film and the film thickness of the anodic oxide film. Was measured. In addition, the micrograph was observed to determine whether or not the primary crystal Si was layer-separated.

The particle size of the primary crystal Si and the film thickness of the anodized film were measured by image processing software (Quick Grain, manufactured by Innotech Corporation).

Whether or not the primary crystal Si is layer-separated is determined by visually observing the primary crystal Si shown in the above micrograph and occupying more than half of the width of the primary crystal Si in a direction substantially orthogonal to the film formation direction. When there were two or more continuous layers, it was determined that the primary crystal Si was layer-separated.

Further, the thermal conductivity of the test pieces 1 to 4 was measured by a laser flash method using a thermophysical property measuring device (LFA 457 MicroFlash manufactured by NETZSCH).

Table 1 shows the measurement and evaluation results (Si content, particle size of primary crystal Si particles, film thickness of anodized film, presence / absence of layer separation, and thermal conductivity) of the test pieces 1 to 4.

The test pieces 1 to 3 in which the primary crystal Si dispersed in the anodized film was layer-separated had a lower thermal conductivity than the test pieces 4 in which the primary crystal Si was not layer-separated.

The aluminum-based alloy material of the present invention has a feature that the thermal conductivity is lower than that of the conventional aluminum-based alloy material having an anodized film. Therefore, when the aluminum-based alloy material of the present invention is formed on the top of the piston for an internal combustion engine and the combustion chamber, preferably on the top and the combustion chamber of the piston for a diesel engine, it is possible to reduce the fuel consumption of the internal combustion engine and to the environment. It is expected to reduce the load and reduce the financial burden on the user.

Claims (3)

An electrolytic solution containing 0.5 mol / L or more and 4.0 mol / L or less sulfuric acid and 0.05 mol / L or more and 0.2 mol / L or less organic acid with respect to the Al—Si hypereutectic alloy. A method for producing an aluminum alloy material, which is subjected to anodization treatment for 5 hours or more. Sulfuric acid of 0.5 mol / L or more and 4.0 mol / L or less and 0.05 mol / L or more and 0.2 mol / L or less with respect to the piston base material for internal combustion engines cast from Al—Si hypereutectic alloy. A method for manufacturing a piston for an internal combustion engine, which is subjected to anodization treatment for 0.5 hours or more with an electrolytic solution containing an organic acid. The method for manufacturing a piston for an internal combustion engine according to claim 2 , wherein the anodic oxidation treatment is applied to at least a wall surface forming the top surface of the piston base material for an internal combustion engine or a wall surface forming a combustion chamber.